I am so NOT the guy who believes in all the extra gas additives. I just fill up at Chevron and call it at day. My 2001 Explorer 4.0 SOHC (108K mi) started having a rough idle, so just for sh**s and giggles, I bought a bottle of gumout regane (stupid name--I really can't believe I bought the stuff) and put it and about 13 gal of gas in the tank. Within 50 miles, the rough idle was gone. Just another anecdotal story with no evidence of anything, but it actually sort of surprised me.